Methods for illuminating documents

ABSTRACT

An arrangement for illuminating objects wherein a large number of objects are rapidly and continuously transported past one or more stations, each illuminated by a cylindrical, integrating Lambertian reflecting/diffusing cavity having one or more like light sources therein so as to generate and project a highly intense, highly uniform and highly diffuse beam of illumination, while incorporating optical guide means to couple said illumination beam to the face of the objects at said station and to couple the reflected image of the object back to the cavity.

This is a Division of U.S. Ser. No. 08/643,393, filed May 6, 1996, nowU.S. Pat. No. 5,717,504, which is a Division of U.S. Ser. No. 08/486,489filed Jun. 7, 1995, now U.S. Pat. No. 5,519,513 which is a Division ofapplication Ser. No. 08/192,964, filed Feb. 7, 1994 now U.S. Pat. No.5,453,849.

FIELD OF INVENTION

This invention relates to arrangements for illuminating objects, andparticularly to such involving an integrating cylinder and associatedillumination-coupling means.

BACKGROUND, FEATURES

Workers in the field of illumination are aware that the art ofilluminating objects (e.g. for imaging thereof) is proceeding apace,with increasing need to more effectively provide intense lighting whichis nonetheless diffused and uniform across a field of view, while alsobeing cost-effective and free of harmful thermal effects.

This invention provides an illumination system that can be useful withan electronic image-capture system, giving a combined platform apt forintegration in a high-speed processor. This platform provides theability to capture a video image of an object as it passes through theprocessor at full speed, and direct the captured image data toadditional electronics which process and compress the captured data. Thedata may then he stored in storage and retrieval systems where it may beaccessed for further manipulation and processing, displayed on videoworkstations, printed (typically using high-definition laser printers),transmitted electronically from point to point, placed in an archivesystem where it may be stored for long periods, or any combination ofthese processes as defined by the system parameters. Such processes, orcombinations of processes, are typically controlled by mainframecomputers which act as “host” systems to link multiple imaging systems,storage and retrieval systems and other peripherals.

The transport systems for which this imaging platform is contemplatedare capable of transporting objects past processing stations at speedsbetween 100 to 400 inches per second (ips, or 2.54 to 10.16 meters persecond mps). The objects, with a typical thickness of 0.005 inches(0.125 millimeters) move along a vertical constraining channel known asa “track,” having a width of typically 0.070 to 0.090 inches (1.78 to2.29 millimeters), known as the “track gap”. This “track gap” is madeconsiderably wider than the width of the object to accommodatevariations due to tolerances and also to accommodate foreign objects(e.g. documents with staples, paper-clips and the like) which inevitablyare attached to such objects from time to time. While this “wide” trackgap is necessary for reliable transport of documents, it creates anadditional problem or depth of field for a potential video imagingsystem. Such system must be able to capture an image of the object (e.g.a sharp focus and with correct illumination no matter where it happensto be located within the track gap. The location of the object withinthe track gap may also change from point to point within the length of asingle object.

The field of view to be captured by an imaging such as the one describedhere is largely defined by the maximum height of the objects (e.g.documents) which must be captured. The objects here contemplated (checksand like financial instruments) are typically between 2.75 to 4.75inches (70.0 to 121.0 millimeters) high and between 6.0 and 10.0 inches(152.0 and 254.0 millimeters) long.

Image capture is achieved by passing the object in front of aphotosensitive device known as a CCPD, well known to workers in the art.This consists of a large number of very small, individual photosensitivereceptors, disposed in a linear array. The object is passed in front ofthe CCPD as a natural function of the object transport, and a completeimage of the object linear segments individually captured from the CCPD,a process known in the art as “line scanning”.

The photoreceptors of the CCPD consist of a semiconductor material whichis formulated to convert incident light into an analogue electricalsignal, which varies in potential depending upon the intensity of theincident light. The captured image thus consists of many individualrecords from each receptor, known as “pixies”, each having a particularanalogue potential which corresponds to the intensity of the incidentlight during the time the individual record was captured.

The time available for a receptor to capture this data is very short. Inthe preferred embodiment, and in other embodiments described e.g. inU.S. Pat. Nos. 5,063,599, 5,003,189, 5,063,461, 5,155,776, 5,144,457,5,259,053 and 5,255,107, the document transport velocity is 300 ips(7.62 mps) and the preferred perceived size of an individual pixel is0.005″ (0.125 millimeters) square. So the time available for theindividual receptor to capture the data related to a particular pixel is0.005÷300 or approximately 17 millionths of a second (17 microseconds).At the maximum velocity (of which the preferred embodiment is capable),this time may be as brief as 12.5 microseconds. This time is known toworkers in the art as “integration time”, since it describes the timeavailable for the photosensitive receptor to gather all the photonswhich have struck its surface and integrate their energy to produce ananalog potential (i.e. electronic image).

The CCPD of choice in the preferred embodiment is the Reticon RL1228D, alinear array device contained in the familiar “chip” -style package,which contains sufficient receptors to allow us to image said documentsat the preferred pixel size and can maintain the necessary data rates(up to 80 megabytes per second) to permit imaging at the preferreddocument speeds. This device is commercially available and attractivelypriced.

It will thus be seen that the selection of the type and intensity of thedocument illumination system is very critical and must be closelymatched to the physical parameters of the document transport and theelectronic characteristics of the CCPD which is to be employed. Theillumination system must provide enough light to produce adequate signalfrom the CCPD under the worst possible conditions for document,transport, CCPD, optics and processing electronics. The illuminationsystem should also provide lighting which is uniform over the entiresurface of the document to be imaged, in order that the CCPD may providea consistent response for a given condition at different points on thedocument. The illumination must also be correctly devised to accuratelyrender the colour and contrast of the document, since the CCDP is amonochrome device which will render images only in shades of grey. Anobject hereof is to teach a means of deriving such illumination.

Because of the potential archival nature of the captured image and themany possible uses to which it will be put, a very high standard oflegibility must be applied. We expect to satisfy the “eyeball test”—thatis, what is visible on the document must be visible in the image. Whilelater electronic processing can remove or suppress selected information,it cannot synthesize data which was not originally captured. Therefore,the illumination must be of sufficient intensity to faithfully renderall significant on the document at the same intensities and contrasts aswould be observed with the human eye.

Conversely, the image should not contain data which is not visible tothe human eye; this might tend to confuse or obscure the imaged datawhich is human-visible. For this reason, the illumination must also bespectrally correct, taking into consideration the spectral response ofthe CCPD (which does not necessarily mimic that of the human eye) andthe effects of any optical elements used in the image camera. Thiscombined response must approximate the response of the human eye, knownto workers in the art as “photopic response.” Failure to match thisresponse may result in startling artifacts in the captured image, suchas images of inks or imprints which are not visible to the human eye butare perceived by the CCPD as a result of its own spectral response, orthe spectral characteristics of the illumination, or both. Suchartifacts are particularly common with the increasing use ofsecurity-motivated imprints and watermarks which are invisible to theunaided eye but which will fluoresce in the visible spectrum whenilluminated at extra-photopic frequencies, such as ultra-violet light.

Although the photopic response is the “baseline” for which we aim, ithas been found that certain carefully-designed alterations to thespectral response of the camera system can enhance the photopic responsewithout adding or subtracting data from the image. For example, a slightadjustment of the spectral response to the red end of the visiblespectrum, combined with modifications to the response curve edge rates,will enhance contrast and legibility of documents printed in multiplesimilar shades of red ink. Similar adjustments may be used to enhanceother specific document styles, as will be well understood by workers inthe art, and may be aided by filter means (e.g. see FiL below).

One drawback of our preferred CCPD device is the size of thephotosensitive array, which is of the order of 0.6 inches (15.0millimeters) long. Since the document may be up to 4.75 inches (121millimeters) high, an optical system, including a lens, is required toreduce the image from the height of the document to fit upon the CCPD.The optical system for capturing the image from the document thusbecomes somewhat more complex, and is generally referred to as a“camera”.

For reasons of stability, ease of construction and cost, we prefer tocombine the illumination system and the image camera into a single unit(an IMAGER) which can be more easily integrated into an existingdocument processing system. Where we want to capture images of both thefront and rear of a document simultaneously as it passes through thesystem, two such illumination/camera units are required, and we preferto further combine both units into a single IMAGER module, whichcontains complete illumination systems and imaging optics/CCPDs for bothfront and rear faces of the document (e.g. see IMAGER embodiment ofFIGS. 2-6). An important goal is to make the parts of the twoillumination systems and cameras identical so far as possible.

Dust

Workers in the art will be familiar with some of the problemsencountered when integrating optical systems into high-speed documentprocessing machinery. The area of the document track and the associatedmachinery to drive the documents (belts, pulleys, rollers, shafts,motors and the like) are typically laden with dust. The dust is producedby the documents themselves, which shed fibers from the friction ofdriving elements and from sheared and cut document edges, and from themany high-speed drive elements such as belts and rollers, which tend toshed rubber and metal particles under continual friction with drivenpaper (which is highly abrasive) at elevated speeds. This material isnot harmful in itself, and the machinery is designed to work unaffectedeven with a considerable buildup. However, dust of any sort in animaging system will rapidly compromise the quality of captured images.If a large fragment finds its way onto some part of the optical system,it will leave undesirable spots or streaks on the images, and a buildupof dust on optical surfaces will lead to a gradual decrease intransmission of images and a consequent loss of legibility or contrastin the captured image. To avoid such undesirable effects, we prefer—asan object hereof—to package the camera, illumination means and imagingoptics in a single IMAGER unit which is hermetically sealed againstdust.

The selection of the light source has a major impact upon the design ofsuch an IMAGER unit, and factors such as the cost, service life,reliability and safety of a given light source have great impact uponits design. In previous work, we have favored the use of high-pressurexenon arc lamps, high-pressure tungsten-halogen incandescent lamps andmultiply reentrant fluorescent lamps to address the lighting needs ofparticular document processors. Previous analysis had suggested thathigh-pressure tungsten halogen lamps were not preferable for providingsufficient light for use at higher document speeds,—but our latestdesigns, coupled with improvements in the amplification and processingof signals from the CCPD, indicate that this is now feasible.Tungsten-halogen lamps of this type offer various advantages over anyother light source we have investigated for these applications. They arevery efficient, produce light well-matched to the desired photopiccamera response, are easily handled by unskilled personnel, are widelyavailable and very attractively priced. They are also well suited to beapplied in illumination systems utilizing an “integrating,” “Lambertian”cylinder to provide intense, uniform illumination. Such is an objecthereof.

Data captured from an imaging camera system of the type described isincreasingly useful for tasks beyond the simple matters of documentviewing and archiving. Various electronic systems are now being employedto read printed and handwritten data on financial instruments such aschecks, with advantages for speedy, automated handling of suchdocuments, as will be well understood by workers in the art. If suchsystems are to be employed, it is highly desirable that imaging camerasof the type described produce data in a consistent format which will notvary substantially from camera to camera. Such recognition systems relyheavily on tables and databases of previous “experience” and such datahas maximum value if it is all rendered from images produced to a commonformat. Most important among the elements of such a format areconsistent magnification and pixel size from camera to camera—that is tosay, cameras of a given type should render details on the same documentto the same size within a very small tolerance range. We prefer to set atolerance on magnification of ±2% for the entire camera system, toensure the best response and highest efficiency from the automatedreading systems presently available.

Such a tolerance may appear liberal until it is understood thatcommercially-available optical components have typically very losetolerances on optical parameters such as focal length and magnification.A tolerance of ±5% is not uncommon on a single component such as a lens,and camera systems of the type described may contain multiple opticalcomponents, each with a significant and additive tolerance. While closertolerances may be obtained, they are always accompanied by higher cost(typically 3× to 6× the cost of the comparable commercial lens) and bythe difficulties and risks associated with the purchase of custom-madecomponents. We have found it preferable to design our camera systemswith provision to adjust various components such that the desiredtolerances of magnification and pixel size may always be achieved evenwith optical components having much larger individual tolerances.

Centration Error

A secondary and specific problem relates to a characteristic variationin commercially-available lens assemblies suited for use in such acamera. Such lenses all exhibit, to a greater or lesser degree, a randomerror known as “centration” error, which may be described as a variationbetween the physical and optical center lines of the lens package. Thiserror will cause similar caner-as, constructed of identical parts otherthan their lenses, to “look” in different places. The source of thiserror is shown schematically in FIG. (6). It will be readily observedthat a misalignment q between the mechanical axis of the lens M—M andthe optical axis O—O will give rise to an error at the document faceequal to (m)×(q), where m is the magnification ratio of the camerasystem. In systems of this type, the magnification ratio is typicallybetween 7 and 10, so any error of centration at the lens could bemagnified by as much as 10× when applied at the image plane. This isobviously a highly-undesirable condition for cameras which are intendedto be easily assembled and replaced, since no two cameras will renderthe same image of the same document. In the worst case, it is possiblethat a camera might fail to see the top or bottom of a maximum-heightdocument. As with variations in magnification/focal length tolerances,lenses may be purchased in which this error is minimized, but it isnever entirely removed and the incremental cost is once againgreat—typically up to 5× the cost of the comparable commercial lens, andthe additional costs for the desired focal-length/magnificationtolerances need to be added to this. Once again, we prefer to eliminatethis error by providing selected adjustments for certain elements of thecamera which allow us to adjust this error to zero.

By means of the preferred adjustments to magnification, pixel size andcentration, we may produce cameras containing individual parts with awide range of tolerances which nevertheless render the same image of thesame document, as regards both image position and pixel size.

Imaging technology as a means of improving document processing ispresently under consideration in the art, e.g., as disclosed in U.S.Pat. Nos. 4,451,619; 4,246,808; and 5,089,713. Generally, such imaginginvolves optically scanning documents to produce electronically encodedimages which are processed electronically and stored on high-capacitystorage media (such as magnetic disk drives or optical memory) for laterretrieval and display. It is apparent that document imaging can providean opportunity to reduce manual handling and manipulation of documents,since electronic images may be used in place of the actual document.

This invention relates to such imaging e.g. teaching packaging a numberof high-intensity, well-cooled, light-source means enclosed in acylindrical integrating Lambertian cavity, and this housed, withassociated optical and CCPD components, in a single, overall sealedIMAGER structure. The taught arrangement is preferably modular, allowingit to be easily installed into a relatively conventional existing objectprocessing system. It will simplify manufacture and service by using aminimal number of common and easily installed components, and byavoiding the use of extensive assembly fixtures and like devices of highaccuracy and cost. An object hereof is to address the various problemsand difficulties described above and to provide the mentioned, andother, features and advantages.

The method and means discussed herein will be generally understood asimplemented, constructed and operating as presently known in the art,except where otherwise specified; and with all materials, methods anddevices and apparatus herein understood as implemented by knownexpedients according to present good practice.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated by workers as they become better understood by reference tothe following detailed description of the present preferred embodimentswhich should be considered in conjunction with the accompanyingdrawings, wherein like reference symbols denote like elements:

FIG. (1) is a front sectional view of a single preferredilluminator/camera assembly embodiment including an integratingLambertian cylinder, enclosing lamp means and packaged in a housingwhich also contains and positions light-conducting means and imagecapture means (CCPD and associated optical means); while FIGS. 1A, 1Bfunctionally illustrate such a cylinder and FIG. 1C shows such incombination with camera means;

FIG. (2) is a side-sectional view of a pair of like (twin-)illuminator/camera assemblies, with a pair of said cylinders, plusassociated light-conducting means and image capture means, combined in asingle IMAGER unit;

FIG. (3) is a plan view of the twin arrangement of FIG. 2;

FIG. (4) is an isometric view showing the front section of the camerashown in FIGS. 1-3;

FIG. (5) is a schematic showing an imaging optical path for the cameraof FIGS. 1-4;

FIG. (6) schematically illustrates the aforementioned phenomenon of“centration error” and how it arises; and

FIG. (7) shows an isometric view of an alternative construction of anilluminator/camera (IMAGER) assembly in which a single glass block isemployed to perform the functions of multiple glass blocks and mirrors.This construction is otherwise identical in nature and intent to thatdescribed in FIG. (1).

DESCRIPTION OF PREFERRED EMBODIMENT

Overall document processor concepts will be discussed; followed bydetails of our preferred illuminator/camera embodiment.

General Concept of Preferred Embodiment

FIG. 1A simplistically shows an integrating Lambertian illuminationcylinder unit C that is here preferred. Unit C will be understood toprovide a light source that we have characterized as a Lambertianemitter distributed in a linear fashion. The output will appear as anincoherent source of monochromatic or panchromatic light emitted from anaperture T-S which has a relatively high aspect ratio (length to widthratio). The internal source(s) of luminance may be derived from suchlight sources as; incandescent bulbs, fluorescent lamps, gas dischargelamps, laser sources or other optically pumped emitters or from otherluminous sources such as the output of a fiberoptic bundle—but here weprefer tungsten-halogen lamps. The placement of the source(s) is notcritical, but may impact output uniformity. The intensity profile as afunction of distance from the exit aperture is very uniform andpredictable and allows for a considerable “depth of illumination”.Components comprising the disclosed light source are readily available,easily manufactured from standard materials and do not rely on thecritical placement of any other component.

Method of Operation

A typical application for this light source is viewed in FIGS. 1A, 1Bwhere:

a) A hollow cylinder is provided with an aperture T-S cut along itslength and circumferentially offset from a series of circular apertureswhich allow for the intromission of an array of incandescent lightsources, L;

b) The cylinder interior is coated with a high reflectivity Lambertian(diffuse) reflector-film;

c) The assembly is placed in proximity to a target document d (FIG. 1B)requiring uniform illumination while in motion with respect to thecylinder and

d) Light emitted from the source(s) L is reflected and scattered withvery little loss throughout the entire internal cavity of the cylinder,eventually finding egress at the exit aperture; T-S

Proposed Application

One possible arrangement of this proposed light source is shown in FIG.1C. This end view of the cylindrical source shows;

a) The hollow cylindrical body with its interior coated with a highreflectivity, diffuse material;

b) One of the (potentially many) light sources L used to illuminate theinterior of the cavity and having multiple reflections before it exitsthe cylinder;

c) The “slit” of light positioned in proximity to a document, or otherrelatively flat object, traversing perpendicular to the axialorientation of the cylinder;

d) The light reflected off the object d returns back through the ExitAperture, T-S, then through a Viewing Aperture ts to an Image Lens andis imaged on to the linear array of a CCPD Detector Array (Camera);

e) The scan rate of the CCPD Camera is is synchronized to the linearvelocity of the object so as to take repeated “slices” of the object asit passes in front of the light source.

Advantages of Proposed Light Source

Lambertian characteristics of this light source C; it inherentlyproduces a uniform and glare-free means of illumination—and no focusingof illumination beam needed.

There is no limit on the length of the exit aperture T-S, thereforeproviding an unlimited, uninterrupted, uniform source of illumination.Fluorescent lamps approach this affect but are limited to maximumlengths of about 96 inches before another lamp is overlapped or buttedto the end of the previous one. Slit T-S can be long, while the lampsused are small;

The luminous sources (lamps) L in the cylinder can be selected tooptimize system performance by using incandescent sources if an“Infrared-rich” light source is needed; fluorescent, if a “cooler” lightsource is needed; Ultra-Violet if a UV source is required; or anyselection of other possibly monochromatic sources depending on thesystem application and demands. The output from all such sources ofinternal luminance is integrated in the cylinder to produce a single,uniform beam of light.

Cylinder interior may be coated with a phosphorescent material (insteadof the white reflecting material) which, upon excitation from anappropriate source, will provide a similar uniform output. The colorselection of the phosphor may also lend itself to optimizing systemperformance.

Congruence of the illumination path with the imaging path facilitatessimplified, compact packaging—i.e. image can return alongillumination-path

All illumination is “indirect” (e.g. document can never “see” filament).

First Embodiment, FIG. 1

FIG. 1 shows such an integrating Lambertian cylinder C and associatedCCPD, lens etc., all packaged into one housing H′ which is alsoadapted—according to this embodiment—to house optical guide means gm(glass block GB, GB, and associated mirror surface M) which opticallycouples aperture T-S to the imaging site where documents d are drivenpast. By a further feature, housing H′ is adapted to protrude thru atransport platform MB so that only guide means gm lie above MB, whilethe rest of housing H′ lies below (on the other side).

FIGS. 2-4 depict a twin illumination/camera (IMAGER) unit systemaccording to our preferred embodiment. This IMAGER will be understood asconsisting of two essentially identical camera assemblies (e.g. each asin FIG. 1) combined into a single system, one for the front of thedocument, one for the rear, [like elements in each camera aredifferentiated by the subscript “f” for “front” and “r” for “rear”.]This IMAGER comprises an integrating housing H, with twosource-integrating cylindrical Lambertian cavities C therein. Housing Hincorporates (packages) both illumination means, camera means, andassociated light-coupling and image-coupling means (e.g. glass blocks GBand image mirrors M) for directing light from each cavity C to passingdocuments and likewise coupling the images reflected from the documentsback through the cavity to imaging means (e.g. CCPD) coupled thereto.

Each “integrating” cavity C consists of a cylindrical cavity, open (andcapped) at one end and closed at the other, fashioned in housing H. Theopen end is closed by separate cover CP, permanently fastened to housingH, thus forming a true closed cylindrical cavity.

Glass blocks GB, fitted onto housing H, (preferably two for each cavity,see below and FIG. 3), act to optically guide illumination from cavity Cto the imaging site and back. Image mirrors M, also fitted to housing H,act to optically reflect and direct the image of the document back intohousing H, through cavity C and, via image-forming lens means LL, ontoimaging means CCPD. As a feature hereof, glass blocks GB and mirrors Mwill be seen to advantageously allow source-integrating means,illumination sites and camera hardware to be remotely mounted from theimaging site and physically isolated therefrom, (e.g. preferably underplatform MB), thus preventing the entry of dust and debris into thishardware, facilitating repair-access, and isolating the units thermallyand optically.

As will be evident from FIG. (2), one cylindrical cavity, Cf, may beused for illumination/detection of the front face of the document, whilea second like cavity, Cr, may be used for illumination of the rear facein like manner.

Each cylindrical cavity C contains an array of one or more lamps L eachpreferably a like tungsten-halogen incandescent lamp. Our preferredembodiment shows five such lamps; however more or less, of varyingpower, could be employed depending upon the requirements of any givenapplication. Along the side of each cavity C in housing H is a long,narrow illumination slit T-S adapted to admit a maximum of “integratedlight: from the interior of the cylinder C to respective glass blocksGB, GB and thence to the face of the document d to be illuminated. Theimage of the illuminated document passes back thru glass blocks GB-GB,then it is reflected by image mirror M back through the sameillumination-slit T-S, through the cavity C and beyond, into a second,smaller imaging-slit ts, and thence to lens means LL and camera (CCPD)means.

As a feature of optimization, this image aperture ts should have a widthapproximately that of the CCPD and should be arranged to pass onlyreflected images (from documents)—essentially barring passage of anyraw, non-image light from the cavity; i.e. aperture ts will be “dark”,or opaque to all direct illumination from its cavity. To help make it“dark”, aperture ts will preferably have anti-reflective sides (e.g.roughened, or with fins, etc.) and have a rather collimating length dt(e.g. here 3-4″ or more, see FIGS. 1, 5; where cavity wall is about ¼″thick). Also, opposing illuminating-aperture T-S will include glassblocks which have anti-reflective ends facing the cavity, to minimizereflection to imaging-aperture ts.

It will be noted, in FIG. (3), that two glass blocks GB are showndisposed at equal angles Ω about the optical centerline of the camera.We find that optimal and consistent illumination across the full widthof the track is a function of track width, size and width of glassblocks GB and pf the distance between them, the type and intensity ofillumination and the type and characteristics of the glass blockmaterial. We find that the illumination may be advantageously shaped andformed in the area of the imaging site by increasing or decreasing angleΩ to produce the most consistent result. Workers in the art will readilyunderstand that the multiple variables at play in this area makeanalysis of the construction most complex, and that the best angle for Ω(if other than 0) will be found by careful experiment. This is not tospecify that angle Ω need necessarily have any value other than 0, butrather to say that illumination may be beneficially impacted by carefulexperiment and control of this angle.

The housing H containing cavities C is preferably made of aluminumalloy, and the interior surfaces which form integrating cavities C arepreferably at once highly reflective and also highly diffusing, a dualproperty we characterize as “Lambertian reflectance”. Such reflectingsurfaces will also diffuse and integrate the light from all theindividual lamp means and, by means of many internal reflection paths,produce at the glass blocks GB, GB non-directional illumination ofuniform intensity in which the individual light sources are no longerdiscernable, and their contributions are well intermixed and“integrated”.

Such a reflecting surface is preferably obtained by coating with ahighly diffuse reflecting medium having a matte finish. We prefer to useBarium Sulfate, carried in an inorganic binder; it may readily beapplied to the cavity (preferred aluminum alloy) surfaces to provide anearly perfect Lambertian surface at moderate cost. While housing H ispreferably unitary, it may also be divided (e.g. one front, one Rear; orunitary with separate front, rear optical guide means).

An alternative construction is also possible as shown in FIG. (7),wherein the two glass blocks GB, GB, described above, are replaced by asingle glass block, SGB,—one for each illuminating cavity C. Such classblocks will be understood as provided with mirror coatings and asserving as an illumination-coupling means for conveying light from thecylinder C to the face of the document, and also for conveying the imageof the document back through the cylinder to the lens and CCPD means.

This alternative construction will be understood to be identical in allrespects to that already described, and to be described subsequently,save only the differing detail of the construction and application ofthe single glass block. Such a construction may produce a cameraassembly with fewer parts (such as mirrors, mounts and the like) and asmaller profile in the area above the cylinder.

These advantages should be weighed against the increased cost andcomplexity of such a single glass block, which must incorporatehigh-precision mirror means and selective application of reflectivecoatings, as well as being larger and heavier that the two individualglass blocks. We do not believe that there are significant variations inperformance between the two designs; thus, selection of one over theother, can be made based upon the particular parameters of the design,as understood by workers in the art.

In the embodiments of FIGS. 1-4, documents d may be transported aboveone surface of a machine base-plate is structure or platform MB, pastthe site of image capture (e.g. between front and rear glass block meansGB as FIG. 3), while associated front and rear integrating cylinders Cf,Cr, lamp means, lens means and CCPD means are located below base-plateMB and isolated from one another, from affecting documents and from theentry and build up of dust, debris and the like. Such remote dispositionof lamp, lens and CCPD means also permits them to be easily accessed forservice and repair without need to disturb components on the upper faceof base-plate MB, where typically extensive high-speed rotating machineelements are disposed to drive and direct documents d.

Construction of Illumination Means

Illumination within each cylinder cavity C is provided, preferably, byan array of tungsten-halogen incandescent lamps L, which are chosen fortheir well-adapted spectral characteristics, ready availability,moderate cost and excellent reliability. Further, by using multiple,low-cost lamp means, available in a wide range of illumination outputswithin the same interchangeable package style, we may custom-tailorillumination to a given set of circumstances by selecting more or fewerlamps of varying output to give the exact intensity of illuminationdesired. Additionally, the use of multiple lamps permits us to introducesome redundancy into our system—e.g. adding an “extra” lamp to provide amargin of illumination over what is required, and allowing sensing ofthe failure of a lamp by electronic current-measuring sensing means (notshown, but well known in the art), to occur without “downtime”. That is,we may construct a system whereby the camera may continue to function(within parameters) after one lamp fails; while the unit can report lampfailure to the controlling electronics and warn the attendant to servicethe lamps at the next convenient opportunity.

Cavity Sensor

As a further feature of advantage, we prefer to add an optical sensor OSwhich views some part of the cylinder wall (not looking directly at anyof the lamps) and directs its output signal, OSS, from that sensor tosome signal-conditioning means (not shown, but well understood in theart). In FIG. (2), optical sensors OS are shown mounted in each coverplate CP, (sensor Cr in cover Cpr, sensor Cf in cover CPf). But this ismerely a schematic representation—the sensor may be mounted in anyconvenient position where it has an unobstructed view of the wall of thecavity C, since the highly integrating nature of the cavity means thatany part of its wall has the same brightness as any other part. Thesignal conditioning circuitry should have been initially calibratedagainst a known reference; it can then be used to optimally adjust lampcurrent to give the right amount of light. In this way, optimalillumination may be derived, to secure the best and most consistentresponse from the CCPD, while at the same time minimizing lamp current(thus maximizing lamp life, as well-understood by workers regardingincandescent lamps) and minimizing power consumption and thereforeundesired heating of the camera assembly.

Lamps

In our preferred embodiment, we prefer the use of 5× 35-Watt tungstenhalogen lamps, which we find give adequate illumination for theparticular application we have in mind, (e.g. where document speed isthe order of 300 ips.) Of course, the total illumination required may begreater or less, depending upon document speed, and this may beaccommodated by using lamps of the same package dimensions but of higheror lower power, or by adding/omitting one or more of the lamps, or acombination of both. A feature of advantage of the integrating cylinderdesign is its ability to integrate the output of multiple point-sourcesof illumination to the point where the individual sources are notdiscernable in the final output of the cylinder. This effect holds truefor a wide range of combinations of lamp power and number of lamps.

For ease of construction and service, we prefer to construct theillumination means as a separable assembly, containing lamps, mountingmeans, electrical connection means and cooling means in a single,integrated assembly. In this manner, when warned of a lamp failure, anattendant need not take time to determine which lamp has failed orwhy—but may simply remove and replace the entire illumination assemblywith a minimum of delay. Later, the removed assembly may be re-lampedand serviced at some convenient opportunity. In this way, we ensuremaximum productive uninterrupted use of the document-processing system.

Lamps of this type typically convert a considerable part of their powerconsumption to heat, and a large part of this is transmitted through thebody of the lamp to the mounting and connection means. For this reason,our preferred separable lamp assembly is provided with multiple coolingfins, f—f, so disposed as to lie within the airflow of a separatecooling fan, (not shown, but well understood in the art). A certainamount of heat is also generated in the main housing H, by conductionfrom the lamp assemblies and also as a result of reflective loss at theinner surfaces of cylinders C. Housing H is therefore also preferablyprovided (e.g. FIG. 4) with cooling fins f—f, disposed to lie within theairflow of some (e.g. the same) cooling fan (e.g. see FIG. 1).

Other details and features of advantage.

In our preferred embodiments, we have found it desirable to offset theillumination and mirror means of the front and rear cameras a certaindistance from one another along the document track, typically about1.75″. This offset serves to ensure that the illumination from onecamera assembly does not interfere with the other; e.g. produceuncontrolled or undesirable responses in the other camera. It alsoallows for the provision of document-driving and controlling means (notillustrated, but well-known in the art) between the two camera imagingsites, arranged and adapted to maintain prescribed document speed andlocation, and to improve document control and therefore document imagequality.

Workers in the art are aware that the spectrum falling upon the CCPDmeans may not be optimized for best resolution and rendition of thedocument image, as discussed above. We find that it may be desirable,under certain circumstances, to incorporate into the camera assembly atrimming optical filter (FiL—details not shown, but well understood inthe art) to selectively shape the spectral characteristics of the lightfalling on the CCPD to optimize CCPD response. Such a filter, whereemployed, would preferably be placed as close as possible to the lensmeans LL, since the image is at its smallest at this point and this willminimize the use of costly custom-coated optical filter materials.

In other cases, we have found it feasible to adapt thereflecting/diffusing coating of the inside surfaces of cylinders C toattenuate and/or modify certain wavelengths from the lamps to give adesired spectral output from the cylinder (and therefore to the CCPD)which more closely matches the desired ideal. In such cases, a trimmingfilter may not be required.

In order to eliminate the effects of tolerances within the opticalcomponents (such as tolerances of magnification and centration, aspreviously discussed) we preferably construct the CCPD and itsassociated electronics to be adjustable in various axes in order tocompensate for, or eliminate, these various errors. One suchconstruction is described in U.S. patent application Ser. No.08/064,606, filed May 19, 1993, (and incorporated herein by thisreference), adapted to give sufficient range of adjustment for thisapplication.

Reprise

While integrating illuminating-cylinder arrays are here taught asparticularly advantageous for use with automated, high-speed documentimaging scanners, workers will appreciate that they have utility forother, analogous applications, such as for high-speed imaging orcopying, optical character illumination and/or recognition, traditional“photographic” imaging, or wherever a highly intense, highly uniform,yet diffuse source of illumination is required, and the source is“masked” so as not to be directly “viewed” by a subject or by thecamera.

We considered making the integrating cavity spherical, but for reasonsof practical application to the task of linear illumination, we prefer acylindrical cavity, with multiple lamp source(s) disposed therein toinduce multiple reflections off the inner walls before emission to thedocument site (vs. direct illumination from lamp to document, withoutcylinder wall reflection). In this way, we achieve highly intense,highly uniform, yet diffuse, illumination which is particularly apt forilluminating documents and minimizing any “shadowing” effects (e.g. fromcreases and folds.) We have previously contemplated the use of a highlyrandomized glass-fiber bundle, combined with an accurately focusedarc-lamp illumination means, to achieve the above results (e.g. see ourU.S. Pat. No. 5,003,189), but find that our preferred illuminatingcylinder construction can give superior performance (under certaincircumstances), yet at much reduced cost. Other forms of indirectillumination are suggested in U.S. Pat. No. 4,769,718, although not withan integrating cylinder or the like.

In conclusion, it will be understood that the preferred embodiment(s)described herein are only exemplary, and that the invention is capableof many modifications and variations in construction, arrangement anduse without departing from the spirit of the claims.

For example, the means and methods disclosed herein are also applicableto other, related illumination tasks, both in other imaging-type systemsand to meet other requirements for illumination.

The above examples of possible variations of the present invention aremerely illustrative and accordingly, the present invention is to beconsidered as including all possible modifications and variations comingwithin the scope of the invention as defined by claims appended hereto.

What is claimed:
 1. A method for illuminating and imaging a plurality ofobjects which are rapidly and continuously transported past at least onestation, the method comprising the steps of: providing prescribedillumination means for illuminating said station; arranging saidillumination means to include an integrating structure with at least onecylindrical, integrating Lambertian reflecting/diffusing cavity, thecavity having diffusely-reflecting walls and output port means;providing at least one light source means in the cavity so as togenerate and project a highly intense beam of illumination onto saidwalls to be diffusely reflected thereby and sent to exit at said outputport means, said light source means comprising at least one set oflamps, each set of lamps integrated into a single removable assembly anddisposed so that no lamp directly views said stations; and arrangingsaid output port means to include optical guide means including glassblock means incorporated therein for coupling the diffusely-reflectedlight to illuminate said objects at said station, and for coupling areflected image of said objects back into and through said cavity forimaging thereof.
 2. A method of illuminating a plurality of objectsbeing transported past at least one station, wherein the stations arearranged to have a prescribed respective imaging-site, the methodincluding the steps of: projecting a non-specular imaging beam fromprescribed source means to illuminate the objects passing at saidimaging-site, arranging said source means to comprise: at least one setof lamps, the set of lamps being integrated into a single removableassembly, being disposed so that no lamp directly views saidimaging-site, and comprising at least one or more individual lamps, in arespective integrating Lambertian cavity; an optical glass blockcoupling means adapted to project an illumination of said lamp to saidrespective imaging-site, and back therefrom through said cavity; thelamp being adapted to direct all the illumination to an inner wall ofsaid cavity for Lambertian reflection/diffusion/integration for issuancefrom said cavity as said imaging beam, said inner wall being adapted tointegrate, reflect and diffuse all the light incident upon it to saidoptical glass block coupling means in Lambertian fashion.
 3. In anobject-processing imaging system wherein a plurality of of objects aretransported past at least one imaging station, to be imaged by a cameraassociated with the imagine station, each imaging station having anassociated imaging-site, a method of providing illumination of theobjects, the method comprising the steps of: projecting a respectiveLambertian illumination beam from prescribed source means to saidimaging-site, said source means comprising at least one set of lamps,each set of lamps integrated into a single removable assembly anddisposed so that no lamp directly views said imaging-site; providingmeans for optically coupling object images from said imaging-sitethrough said coupling means to said camera means, said coupling meansincluding a glass block; arranging said source means to comprise aLambertian integrated cavity with said set of lamps disposed therein andto have Lambertian reflecting/diffusing inner cavity-wall means adaptedto project, through an associated illumination slit, a highly-diffused,highly uniform non-specular, Lambertian illumination beam to saidimaging site and back, and arranging said coupling-means to includereflector mean to receive an image reflected from said object backthrough said Lambertian cavity then out, via camera-slits providedtherein, to said camera means; said camera means being incorporated withthe source means in a common housing, being optically coupled via saidcoupling means to an associated image-slit in cavity walls so that thereflected image is passed back from said object through saidillumination slit, through said cavity and through said image-slit tosaid camera means.
 4. A method for illuminating and imaging an object,the method comprising the steps of: providing a light-integrating cavityhaving a plurality of diffusely-reflecting walls, and anillumination-slit through which a non-specular, Lambertian beam ofintense, uniform light is to be projected to said object from saidcavity; providing source means arranged and adapted to projectprescribed illumination onto said walls, to be diffused and reflectedthereby, and to form said Lambertian beam; said source means comprisingat least one set of lamps, each set of lamps integrated into a singleremovable assembly and disposed so that no lamp directly views saidobject; providing glass bock optical coupling means coupling saidLambertian beam to said object; providing camera means and associatedimage-port means through said cavity wall arranged and disposed to passan object image, reflected back through said coupling means, saidillumination-slit and said cavity, to said camera means; and disposingsaid illumination slit opposite said image port means, and in-linetherewith; said camera means being incorporated with the source means incommon housing means, being optically coupled via said coupling means tosaid associated illumination-slit in said cavity walls to that reflectedimages are passed back from said object through said cavity and backthrough said illumination-slit to said camera means.